Easy experience points
Gamble in a casino and play roulette. No matter if you win or lose, you will gain 100 experience points.

Easy "Outstanding Orator" achievement or trophy
When your Speech is at 40, go to Camp Golf, by Lake Las Vegas. Accept the quest from the sergeant. Agree to O'Hanran's method and convince everyone, with Mags being the last. After convincing Mags to play nice, accept her method and go to the gun range. Help them with their guns (45 skill required), and wait for them to start walking back to their tent. Talk to Razz and ask about squadmates. The speech challenge should still be there. You can easily unlock the "Outstanding Orator" achievement or trophy, as well as experience points in increments of 40. When you are done, talk to the sergeant to complete the quest or talk to O'Hanran and ask about the squad. Note: You have the option of helping them with explosives after the guns.

Star Wars reference
Go to the town of Nipton. Walk to the right of the town hall's front entrance to find a burned out building, with a pair of burned corpses in front. The view resembles the scene from Star Wars where Luke Skywalker finds the bodies of his Aunt Beru and Uncle Owen.

Unlimited caps

* In Guardian Peak you will meet an NCR soldier who is wounded. Through some Speech checks, you can get him to give you his gun for escorting him out of the cave that he is in. When you get to the entrance of the cave with him in tow, he will speak and you can continually ask for his rifle, which he will give you along with ammunition. Note: This is best done after earning the perk that allows for over encumbered fast travel.

* Note: This requires the unpatched version of the game. Begin going through the storyline, once you get to Prim and complete the quest there, leave for awhile and return. You will be able to gamble. In order to gamble you must purchase chips. Go to the cashier at the Vikki & Vance Casino. Purchase as many chips as possible with any of the three types of money (Caps, NCR, and Legionaries). Once you have the chips, save the game normally (not by auto-save). Note: Each chip is worth one cap, so you can trade all the chips back for a full refund if needed. Once your game is saved, talk to the cashier again and select the fourth option (something similar to "Cash in my chips"). She will ask what form of payment you want. Pick any option desired, then quickly exit the conversation. This should have given you as much of the form of money you requested that equals to chips. Caps are 1 chip to 1 cap. NCR are 8 chips to $20 and 40 chips to $100, and Legionaries are 4 chips to one Denarius, 20 chips for a Dalhali, and 100 chips for a Aureus. Once you have exited the conversation, check your inventory. You should have the money and the chips still in your possession. Talk to the cashier and repeat the trick. If you want to get higher amounts at a time, do the trick with caps a few times, then buy 1,000 chips for 1,000 caps about five or six times.

* After completing the Sexbot quest, go to the atomic wrangler and talk to Fisto. Choose the "Maybe later" response to get 10 caps. You can continue to do this as many times as desired. With enough time and patience you can accumulate a large amount of caps.

Unlimited experience
Note: This requires at least a 35 Medicine skill. Once your character gains access to the main strip, find Victor outside the Lucky 38 casino. He will tell you that Mr. House wants to meet you. Follow him inside and go up the elevator. Speak with Mr. House (the giant television face that looks like Howard Hughes). Find the dialogue choice pertaining to needing to ask him a few questions. Then, ask "Who exactly are you, Mr. House?", then select "You appear to be a computer, not a man". After that, select the Medicine skill check response, "The lifespan you're claiming is impossible, except for ghouls and super mutants." After that, you will be awarded 35 experience points (or 39 experience points if you have the Swift Learner perk). You can repeat this as many times as desired.

Monorail entry
In Camp McCarran where the monorail directly to the strip is located, you can gain entry to the monorail. Take the long way around and stay as close to the vending machines as possible. Follow the wall around the back way. Make sure the other soldier has his back to you. Crouch and sneak up to this soldier. You may hear the phrase indicating that if you get any closer they will have to shoot you. However, as long as you remain hidden, it may flash "Detected" briefly for a few times. As soon as you are close enough to the door, you can go through it and take a monorail directly to the strip. This may require a few attempts. Be careful when returning to the monorail from the strip. You will probably be shot. However as soon as you enter the monorail it resets, and you can again ride it back to the strip. By using this trick you can bypass many annoyances and quests, and can skip directly to meeting Mr. House and finding the person who shot you.

Enemies catch on fire without firing weapon
Use the .50 machine gun incendiary ammunition on the anti-materiel rifle. Target an enemy with V.A.T.S. The enemy will catch on fire, even if you do not fire the weapon.